Human serum contains a group of proteins that bind to DNA. Our laboratory initially isolated these proteins quantitatively by using affinity chromatography on DNA-cellulose. The preparative method was adapted to handle small serum samples to facilitate screening clinical specimens for abnormalities in these proteins. The results of the screen provided a basis for choosing specific DNA-binding proteins to be isolated individually and characterized. The two major DNA-binding proteins in human serum have been purified to homogeneity. The proteins have been characterized as to important structural parameters such as molecular weight, amino acid and carbohydrate content, etc. The specificity and function of these proteins is being investigated. Radioimmunoassays are being developed to quantitative their serum levels in various diseased states. A DNA-binding protein in malignancy-associated human serum has been purified and characterized. Immunochemical studies have revealed that this protein is a fragment of human complement component C3. The radioimmunoassay for this protein indicates that it has definite potential as a prognostic indicator in the chemotherapeutic management of malignant diseases. The potential of quantitating serum ribonuclease for use in the prognosis or diagnosis of malignant disease is also being investigated. BIBLIOGRAPHIC REFERENCES: Parsons, R. G., R. L. Longmire, S. O. Hoch and J. A. Hoch. 1977. A clinical evaluation of serum C3DP levels in individuals with malignant diseases. Cancer Res. 71: 692-695. Hoch, S. O. & E. McVey. 1977. Purification and characterization of the two major DNA-binding proteins in human serum. J. Biol. Chem. 252: in press.